Method for liquid-developing an electrostatic image

ABSTRACT

An electrophotographic liquid-developing method comprising controlling the polarity of the toner by varying the temperature of the developer solution. An electrostatic charge-substrate having an electrostatically charged latent image is immersed in the developer solution to convert such latent image into a visible image. The developer solution comprises a toner consisting of pigment particles and at least one resin selected from the group consisting of alkyd resin, phenol resin and vinyl resin, and a carrier liquid in which said toner is dispersed. The carrier liquid comprises at least one dispersion medium having different affinities to said resin depending on the temperature.

United States Patent VOLTAGE f Kasuya et a1. Nov. 6, 1973 [54] METHOD FOR LIQUID-DEVELOPING AN 3,220,830 11/1965 Kashiwabara 117/37 LE ELECTROSTATIC IMAGE 3,251,687 5/1966 Fohl et al 252/621 3,296,140 1/1967 Zabiak 252/62.1 Inventorsl Kaluhlko y Kanagawa; 3,356,498 12/1967 Moe et a1... 117 37 LE Wasabpro Ohta; Zenjiro Okuno, 3,357,828 12/1967 Moe 117/37 LE both of Tokyo, all of Japan 3,438,904 4 1969 Wagner... 117/37 LE 3,444,083 5 1969 Oliphant 117 37 LE Asslgneel Kabushlkl Kalsha Rlcoh, Tokyo 3,640,751 2 1972 Kasuya et al. 117 37 LE Japan [22] Fi Sept 20 1971 Primary Examiner-William D. Martin Assistant Examiner-M. Sofocleous 1211 Appl' 182,176 Att0rney-W0odhams, Blanchard & Flynn Related US. Application Data [63] Continuation-impart of Ser. No. 772,242, Oct. 31, [57] ABSTRACT 1968, Pat. No. 3,640,751. An electrophotographic liquid-developing method comprising controlling the polarity of the toner by [30] Foreign Application Priority Data varying the temperature of the developer solution. An

Nov. 6, 1967 Japan 42/70991 eleetrostatie charge-Substrate having an electrostatically charged latent image is immersed in the developer 52 mg 117 37 LE, 9 1 LY, 252 1 solution to convert such latent image into a visible im- 51 Int. Cl. G03g 13/10, 003 9/04 g The developer solution comprises a tener consist- 5 Field of Search 7 37 9 ing of pigment particles and at least one resin selected 118/637 DIG 23; 355/10; 252/62 1 from the group consisting of alkyd resin, phenol resin and vinyl resin, and a carrier liquid in which said toner [56] R f n Cit d is dispersed. The carrier liquid' comprises at least one UNITED STATES PATENTS dispersion medium having different affinities to said 3,507,679 4/1970 Metcalfe et a1 117 37 LE resm dependmg the temperature 3,058,914 10/1962 Metcalfe et al.... 117/37 LE 7 Claims, 1 Drawing Figure 1.1.1 1 9 E .1 CD

THICKNESS VOLTAGE f Vmmmzss VOLTAGE METHOD FOR LIQUID-DEVELOPING AN ELECTROSTATIC IMAGE CROSS-REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a novel method for liquiddeveloping in electrophotography, in which a visible image can be obtained as a negative or a positive selectively on an electrophotographic copying sheet or recording sheet after an electrostatic latent image is formed thereon in a conventional manner. In particular, it relates to a liquid-developing method in electrophotography in which the polarity of a toner having certain ingredients is adapted to be controlled by varying the temperature of said carrier liquid.

The term electrostatic image which may appear in the following description is defined as an electrostati cally charged latent image on an electrostatic chargesubstrate like an electrophotographic copying sheet or an electrostatic recording sheet, which may be convertible to a visible image by proper development.

2. Description of the Prior Art Liquid-developing methods known in the art are the so-called positive-to-positive developing method in which a charged latent image on a copying sheet or a recording sheet is developed in a developer containing a dispersed toner which is charged in the opposite polarity to the latent image, and the so-called negative-topositive developing method in which an electrostatically negatively charged latent image on a copying sheet or a recording sheet is developed in a developer solution in which is dispersed a toner having the same polarity as the latent image area. The developer solution used in the aforesaid methods normally comprises a condensed toner which is a mixture of pigments, a polarity-control agent (asphalt, rosin or synthetic resin are'generally used) which gives a positive or negative charge to the pigment particles used and a small amount of a solvent, and a dispersion medium (which constitutes the carrier liquid) of a high electric resistivity of more than l'fl.crn and a low dielectric constant of less than 3, in which said toner is dispersed. The toner is required to have a charge of distinct polarity in the carrier liquid and sufficient electric potential for adhering, by electrophoresis, to the electrostatic latent image area on the'copying sheet. In practice, however, a combination of pigment, polarity-control agent and the carrier liquid that will comply with the aforementioned requirements is still being sought through trial and error, though some specific combinations have been disclosed in the prior art. Only a limited number of specific combinations of certain kinds of condensed toners and the carrier liquids therefor have been put on the market and their use has been specified for either positive-to-positive development or negative-topositive development. Furthermore, the developer solutions must be made in at least two different kinds depending on whether the electric potential in the electrostatic latent image area of the copying sheets is negative or positive.

SUMMARY OF THE INVENTION Unlike the developing methods hereinabove described, in which a positive image or a negative image is formed by a specific combination of copying sheets or recording sheets and the developer solution, the primary objective of the present invention is to provide a unique liquid-developing method for converting an electrostatic latent image on a sheet into a visible image as a positive or a negative selectively by controlling the electric charge of the toner to be positive or negative,

by changing the temperature of said carrier liquid.

In otherwords, in a developer solution according to this invention there are used a condensed toner in which at least one kind of alkyd resin, phenol resin and vinyl resin is applied to the pigment particles for controlling the polarity thereof, and a carrier liquid which is a mixture of dispersion media having a peculiar affinity to the aforementioned resins, so that the electric charge of the toner can be desirably controlled by varying the temperature of the carrier liquid. Furthermore, the electric charge of the toner can be varied in that way even if the carrier liquid contains only one dispersion medium by changing the temperature of the carrier liquid.

The present invention will be described in further detail with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE shows the relationship between the thickness of the adsorption layer (consisting of a part of a resin as a polarity-control agent and two kinds of dispersion media) with which pigment particles are covered and the electric potential of toner consisting of the resin and pigment.

Curve-l in FIG. 1 indicates the relationship between the thickness of the adsorption layer and the electric potential of resins in general, while curve 2 shows the same relationship for special resins that will create variations depending on the kind of polarity-control agents used. Our experiments proved that a toner in which the carbon black is coated with the alkyd resins shows changes as shown in curve 2 and that a toner in which carbon black is coated with asphalt or rosin varies as shown in curve 1. These facts indicated an adjustability of the thickness of the adsorption layer corresponding to said curve 2 by varying the dispersion media or temperature. It was thus discovered that a suitable mixture of (l) a dispersion medium having greater afiinity and (2) a dispersion medium having smaller affinity to the adsorptionlayer consisting of alkyd resin, or that variations in the temperature of such mixture or the carrier liquid, will change the thickness of the alkyd resin layer adhered to the carbon black, whereby the electric charge of the toner is variable either from negative to positive or vice versa. It was further discovered that these facts hold true also with phenol resin and vinyl resin.

Some of possible disperion'media having a large affinity to the alkyd resin, phenol resin or vinyl resin are partially or entirely halogenated hydrocarbons such as C C1 (C CL F) CI-IClF CCl FCClF or aromatic hydrocarbons such as toluene, benzene, petroleum hydrocarbon including aromatic ingredients, for example, Naphtha No. 6, Solvesso 100, Solvesso (all are products of Esso Standard Oil Co.) and ligroin. The dispersion media having smaller affinity to the aforesaid resins include, for example, such isoparaffinic hydrocarbons as Isopar G, Isopar H (products of Esso Standard Oil Co.), Su'per-VM&P Naphtha (product of Shell Oil Co.) and paraffinic hydrocarbon such as normal paraffins, like n-hexane. The halogenated hydrocarbon include two types; namely chlorofluoro-hydrocarbon such as Daiflon S-1 (CCl F), Daiflon S-3 (CCl FCClF Daiflon S2 (CCI F) and chlorinated hydrocarbon (CCl lsopar G is a petroleum hydrocarbon containing 99 volume percent of isoparaffinic hydrocarbon. Isopar H is a petroleum hydrocarbon containing 99 volume percent of isoparafiinic hydrocarbon. Solvesso 100 is a petroleum hydrocarbon containing 98 volume percent of aromatic hydrocarbon. Solvesso 150 is a petroleum hydrocarbon containing 97.3 volume percent of aromatic hydrocarbon. Naphtha No. 6 is a petroleum hydrocarbon containing 25 volume percent of aromatic hydrocarbon and 70 volume percent of paraffinic hydrocarbon. Super Naphtha is a petroleum hydrocarbon containing vol ume percent of aromatic hydrocarbon and 80 volume percent of paraffinic hydrocarbon.

Ligroin is refined solvent naphtha having a density of 0.850 to 0.870 and a distillation range at 760 mm; percentage recovered at 130C. not more than 5; percentage recovered at 145C. not less than 90; end point not above 155C.

However, the degree of affinity may be varied even in the aforementioned groups of dispersion media having greater or smaller affinities. For example, the polarity control of the toner is possible by a combination of Daiflon S2 and Daiflon S 3 in the group of chlorofluoro-hydrocarbons and by subsequent variation of their temperature. Therefore, in the present invention, the degree of affinity is referred to only in a relative sense.

The alkyd resins which may be used in the process of the present invention include Super Becksol J1350, J-l35l and J-57l which are long oil alkyd resins modified with soya-bean oil, Super Becksol J-537 which is a long oil alkyd resin modified with sunflower oil (the products of Dainippon Ink and Chemical Incorporated). Among the phenol resins are Nikanol PIP-100 (manufactured by Japan Gas-Chemical Co., Inc.), Tamanol 520 (manufactured by Arakawa Forest Chemical Industries Ltd. Japan), PP810 (Gun-ei Chemical Industry Co., Ltd. Japan), Super Becasite 100 (manufactured by Dainippon Ink and Chemical Incorporated), and as the vinyl resins, polymers or copolymers obtained from acrylic acids, methacrylic acids and other vinyl monomers, such, for example, as laurylmethacrylate dimethyl or diethyl aminoethylmethacrylate resins, and laurylmethacrylate styrene resins, are used.

The pigment particles which may be used in the process of this invention include such well-known pigments as carbon black, aniline black and spirit black.

As described above, it is the object of the present invention to provide a method for developing a positive or negative electrostatic latent image on a copying sheet or a recording sheet into a desired corresponding visible image, which may be either positive or negative, using a developer solution prepared by dispersing the aforesaid concentrated toner into a carrier liquid consisting of at least one dispersion medium having a different affinity to alkyd resin, phenol resin or vinyl resin, said method comprising controlling the charge of said toner by changing the temperature of said carrier liquid. Thus, the method of this invention has an advantage that either a positive or negative image as desired may be formed on the copying paper or recording paper from the same original if such concentrated toner and at least one of dispersion media are prepared.

EXAMPLE 1 A concentrated toner was prepared by adding to 5 grams of the pigment particles (Mogul A, carbon black manufactured by Cabot of the U.S.A.) 20 grams of alkyd resin (a long oil alkyd resin manufactured by Dainippon Inc. and Chemical Incorporated under tradename of Super Becksol J1351) and 100 grams of toluene and ball-milling the mixture for more than 10 hours.

Three types of electrophotographic developer solutions were prepared by dispersing approximately 1 gram of the concentrated toner in 100 ml respectively of the following carrier compositions:

a. Carrier liquid consisting of a mixture of dispersion media composed of equal parts of Daiflon S (CCl F-CCl F) and Daiflon S (CCl F) b. Carrier liquid consisting of a mixture of dispersion media composed of one part of Daiflon S and 2.33 parts of Daiflon S 0. Carrier liquid consisting of a mixture of dispersion media composed of one part of Daiflon S and 9 parts of Daiflon S The toner in the above carrier liquids (a) and (b) was charged positively at room (25C.) temperature, but in the case of the carrier liquid (0), it was found that the toner was charged negatively. When the developer solution (a) was cooled to 5C. and when the developer solution (b) was cooled to +5C., each of the toners was charged negatively, while in the developer solution (0) the sign of the charge did not change to positive even when the solution was heated to 40C.

EXAMPLE 2 A concentrated toner was prepared by mixing 5 grams of the pigment particles (Mitsubishi No. 44,? 356611 black nifiufactured by Mitsubishi Kasei) with 10 grams of 50 percent toluene solution of laurylmethacrylate dimethylaminoethylmethacrylate resin (at a polymerization molar ratio of to 10), 1 gram of manganese naphthionate (containing 10 percent Mn) and 34 grams of Isopar H and ball-milling the mixture thus formed. 0.5 gram of concentrated toner was then dispersed in ml of Isopar H, thereby obtaining a developer solution. This developer showed a positive charge at room temperature but the charge was negative when the solution was heated to 60C. and thereafter suddenly cooled down to 10C.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a method for liquid developing an electrostatic latent image to form a visible image by immersion in a liquid developer comprising a dispersion of an electrically charged toner in a carrier liquid, said toner comprising fine particles of pigment coated with a resin selected from the group consisting of alkyd resin, phenol resin and vinyl resin, said carrier liquid consisting of a dispersion medium selected from the group consisting of (CCl F) CCl F, (CCI F CClF CHCIF perchloroethylene, petroleum hydrocarbon containing about 99 volume percent of isoparaffinic hydrocarbon, it

ligroin, petroleum hydrocarbon containing about 98 volume percent of aromatic hydrocarbon, petroleum hydrocarbon containing about 25 volume percent of aromatic hydrocarbon and 70 volume percent of paraffinic hydrocarbon, petroleum hydrocarbon containing volume percent of aromatic hydrocarbon and 80 volume percent of paraffinic hydrocarbon, toluene, benzene, and mixtures thereof, the improvement comprising changing the temperature of the carrier liquid in order to change the polarity of the toner.

2. The method as claimed in 1, wherein the temperature of said carrier liquid is changed within the range from the freezing point up to the boiling point of said carrier liquid.

3. The method as claimed in 1, wherein said toner consists of alkyd resin, and said carrier liquid is composed of chlorofluoro-hydrocarbon of the formula CCl F) CCl F, (CCl F-CClF or CHClF and wherein the temperature of said carrier liquid is changed within the range of 5C. to 40C.

4. The method as claimed in 3, wherein said chlorofluoro-hydrocarbon consists of a mixture of CCl F-CClF and (CCl F) and the mixing ratio by volume of CCl F-CClF and (CCI- F) is l to I and wherein said temperature is changed within the range of room temperature to 5C.

5. The method as claimed in 3, wherein said chlorofluorohydro-carbon consists of a mixture of CCl F-CClF and (CCl l-'-') and the mixing ratio by volume of CCl FCClF and (CCl F) is 2.33 to l and wherein said temperature is changed within the range of room temperature to 5C.

6. The method as claimed in 3, wherein said chlorofluoro-hydrocarbon consists of a mixture of CCl l=CClF and (CCl F) and the mixing ratio by volume of CCl FCClF and (CCl F) is 9 to l and said temperature is changed within the range of room temperature to 40C.

7. The method as claimed in I, wherein said toner consists of methacrylic resin, wherein said carrier liquid is composed of isoparaffinic hydrocarbon and wherein said temperature of said carrier liquid is changed in the range of 10C. to 60C. 

2. The method as claimed in 1, wherein the temperature of said carrier liquid is changed within the range from the freezing point up to the boiling point of said carrier liquid.
 3. The method as claimed in 1, wherein said toner consists of alkyd resin, and said carrier liquid is composed of chlorofluoro-hydrocarbon of the formula CCl2F)2, CCl3F, (CCl2F-CClF2) or CHClF2 and wherein the temperature of said carrier liquid is changed within the range of -5*C. to 40*C.
 4. The method as claimed in 3, wherein said chlorofluoro-hydrocarbon consists of a mixture of CCl2F-CClF2 and (CCl2F)2 and the mixing ratio by volume of CCl2F- CClF2 and (CCl2F)2 is 1 to 1 and wherein said temperature is changed within the range of room temperature to -5*C.
 5. The method as claimed in 3, wherein said chlorofluorohydro-carbon consists of a mixture of CCl2F-CClF2 and (CCl2F)2 and the mixing ratio by volume of CCl2F-CClF2 and (CCl2F)2 is 2.33 to 1 and wherein said temperature is changed within the range of room temperature to 5*C.
 6. The method as claimed in 3, wherein said chlorofluoro-hydrocarbon consists of a mixture of CCl2F-CClF2 and (CCl2F)2 and the mixing ratio by volume of CCl2F-CClF2 and (CCl2F)2 is 9 to 1 and said temperature is changed within the range of room temperature to 40*C.
 7. The method as claimed in 1, wherein said toner consists of methacrylic resin, wherein said carrier liquid is composed of isoparaffinic hydrocarbon and wherein said temperature of said carrier liquid is changed in the range of 10*C. to 60*C. 